The objective of this proposal is to measure the molecular mobility of various components of the cell surface in "normal" mouse fibroblasts in culture as compared to their virus transformed counterparts. This will be done by studying both the polarization of emission (for rotational mobility) and time correlations in emission (for translational mobility) from fluorescent probes specific for the cell surface. A fluorescence microscope capable of detecting light from restricted areas, as small as 1 micron in diameter, of the cell periphery will be employed. Studies will begin with measurements on single normal and transformed cells as a function of phase in the cell cycle and be extended to cells in contact situations. Such measurements should extend our grasp of the principles governing the motions of cell surface macromolecules. Insight into the role of dynamic cell surface in cell-cell recognition phenomena should also be gained. In particular, it is hoped the proposed measurements to characterize aspects of cell surface dynamics will shed light on the altered social behavior of neoplastically transformed cells in culture.